(1) Field of the Invention
The present invention relates to an apparatus for loading and unloading a workpiece into or from a machine tool.
(2) Discussion of the Prior Art
FIGS. 1 and 2 show a conventional apparatus for automatically loading and unloading a workpiece between a working position in a machine tool and an outside of the machine tool. In this apparatus, a rotational shaft 3 is supported to be rotatable about its axis on a support base 2 which is fixed on a work head 1. The rotational shaft 3 is disposed so that its axis is parallel with an axis O of a work spindle. This rotational shaft 3 has at one end a lever 4, which is fixedly supported on the one end of the rotational shaft 3. The lever 4 is connected at the other end with a cylinder 5, which is provided for rotating the rotational shaft 3 in such a manner that the rotational shaft 3 can be rotated in a clockwise direction or a counterclockwise direction within a required rotational angle in response to an expansion or a contraction movement of the cylinder rod which is caused by actuation of the cylinder 5.
The other end of the rotational shaft 3 is fixed with a bracket 6. The bracket 6 has an installation surface which extends in a direction normal to the axis O of the work spindle. On the bracket 6, there are provided a pair of workhands 7a, 8a. These pair of workhands 7a, 8a are provided to be slidable in a direction normal to the axis O of the work spindle through a pair of guide bars 7b, 8b. The guide bar 7b guides the workhand 7a along an inclined line in an up-and-down direction, and the guide bar 8b guides the workhand 8a along a vertical line in an up-and-down direction. There are further provided a pair of cylinders 7c, 8c. These pair of cylinders 7c, 8c are connected with the workhands 7a, 8a. The workhands 7a, 8a are actuated to be able to shift on the guide bars 7b, 8b by the cylinders 7c, 8c, respectively.
The workhand 7a, the guide bar 7b, and the cylinder 7c constitutes a loading arm unit 7. To the contrary, the workhand 8a, the guide bar 8b, and the cylinder 8c constitutes an unloading arm unit 8. The loading arm unit 7 and the unloading arm unit 8 are disposed on the same plane which is located normal to the axis O of the work spindle. Further, the loading arm unit 7 and the unloading arm unit 8 are spaced with each other so that the axis of the loading arm unit 7; i.e. the axis of the guide bar 7b, and the axis of the unloading arm unit 8; i.e. the axis of the guide bar 8b, intersect with each other at an inclined angle .theta.'. This is for preventing the loading arm unit 7 and the unloading arm unit 8 from interfering with each other in each loading or unloading operation.
In such an apparatus constituted as described above, in order to grip an unfinished workpiece W conveyed at an waiting position A located outside a machine tool, the rotational shaft 3 is rotated to change the direction of the loading arm unit 7 in such a manner that the direction of the loading workhand 7a points to the unfinished workpiece W disposed outside of the machine tool. Then, the workhand 7a is lowered to grip the workpiece W. After the workhand 7a grips the workpiece W, the workhand 7a is raised, and then, the rotational shaft 3 is rotated again to change the direction of the workhand 7a to the beginning position. That is, the rotational shaft rotates until the direction of the workhand 7a points to a working position B.
Furthermore, at the condition that, while the workhand 7a keeps holding the unfinished workpiece W for the next working operation, the unfinished workpiece W is already loaded on the working position B by the previous loading operation, the working operation in which the manufacturing of the workpiece W, which is already loaded by the previous loading operation, is commenced. When this working operation is completed, the unloading arm unit 8 begins its unloading operation. That is, the unloading arm unit 8 is disposed exactly above the working position B, and the workhand 8a of the unloading arm unit 8 is lowered to grip the finished workpiece W finished in this working operation. The workhand 8a is raised after the workhand 8a gripped the finished workpiece W.
After these operation, the workhand 7a which has kept holding the next unfinished workpiece W is lowered to release the unfinished new workpiece W on the working position B. The workhand 7a is raised to the initial upper position after the unfinished new workpiece W is loaded on the working position B.
Then, the rotational shaft 3 is rotated to change the direction of the unloading arm unit 8 in such a manner that the direction of the workhand 8a is turned toward position A located outside the machine tool. The workhand 8a is lowered to release the finished workpiece W, which is finished in the previous working operation, to the position A located outside the machine tool. The workhand 8a is raised until it returns the initial position after the unloading of the finished workpiece W is finished. After that, the workhand 7a of the loading arm unit 7 is lowered to grip a next-conveyed unfinished workpiece W. By the completion of these operations, one cycle operation designed for performing the loading and unloading the workpiece is completed. After that, the same cycle is continuously repeated.
Moreover, the direction changes of the loading arm unit 7 and the unloading arm unit 8 are carried out simultaneously since the loading arm unit 7 and the unloading arm unit 8 are installed integrally with the same bracket 6. That is, the loading arm unit 7 and the unloading arm unit 8 rotate together with each other by keeping the angle .theta.' formed between the axis of the guide bar 7b of the loading arm unit 7 and the axis of the guide bar 8b of the unloading arm unit 8.
However, in the arrangement of the above apparatus, the loading arm unit 7 and the unloading arm unit 8 are provided so as to be disposed in the same plane which is normal to the axis O of the work spindle, and are spaced with each other so that the axis of the loading arm unit 7 and the axis of the unloading arm unit 8 intersect at the angle .theta.', therefore, as shown in FIG. 1, the top part of the loading arm unit 7, which is a free end of the loading arm unit 7 rotatable about the axis of the rotational shaft 3, protrudes toward an outside of the machine tool. The condition shown by the solid line in FIG. 1 corresponds to the initial or usual standstill position of the machine tool. On the side that the upper part of the loading arm unit 7 inclines, there is usually provided a space for a worker who watches, administers or maintains the machine tool. Therefore, the protrusion of the upper part of the loading arm unit 7 becomes an obstacle for the worker, thus, the worker could not approach the machine tool in order to watch or administer or maintain the machine tool.
Furthermore, in the case that a diameter of the workhand 7a or 8a required for gripping the workpiece W becomes large, it has to be designed so that the angle .theta.' between the loading arm unit 7 and the unloading arm unit 8 becomes large as the diameter of the workhand 7a or 8a becomes large. It results in worsening the above problem. Namely, it becomes more difficult for the worker to approach the machine tool.